GIMP Version: 2.8.4
Operating System: Windows
OS Version: Vista
GIMP Experience: Beginner Level

List any relevant plug-ins or scripts:
Separate +

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I have to supply a Chinese printing company with a CMYK file to print 30 vinyl banners...

Im using The Gimp 2.6 and I have to provide the image in CMYK format 772dpi

This is the first time I am sending a CMYK file, so I want to make sure its right, as on my computer screen, the exported image is black and white and inverted (darks are light)

I installed the Separate + plug in and I am using the separate export menu in the 'Image' dropdown menu in Gimp.

There are a few options when exporting, but I have no idea which ones I should use...
When exporting I have the choice of 'Embed Color Profile'
1. None
2. CYMK default profile
3. Print Simulation Profile
4. Own Profile : AGFA : Swop Standard

Which one is best for the printing company???

Should I select format...
1. Tiff
2. Photoshop PSD


Any help is greatly appreciated! These banners are expensive so I cant afford to print them twice

I'm not an expert, but the most common file types that support CMYK are .PSD, .EPS, .TIFF and .JPG files.
So why not save both a .TIFF and a .PSD.

A 772 dpi image will be enormous. For example an A4 image will be 450 MB.
Have a look at the first part of this post, it has some good links on Separate + and CMYK info.
Subject: GIMP - Technical Graphical questions

WOW half a gig for A4 and I need a 5 foot by 2 foot image!!!

I would query that 772 dpi, probably a typo. I was looking at a Chinese publishing site just a couple of days ago. Nice description of offset printing but some of the language was "quaint"

CMYK in Gimp is a not wonderful. This is a video demo I made for someone else, It is Gimp 2.8 but same operation in Gimp 2.6

http://www.youtube.com/watch?v=2rby7r771D4&hd=1

A good bet is to upgrade to Gimp 2.8 and consider the Partha version which AFAIK comes with the separate+ plugins.

If you use Gimp and export your image, then tiff, jpeg and psd are options. However separate+ will only import CMYK tiff. Not a bad idea to stick with that format.

Other options,
Much mentioned recently, Krita, open a RGB image, change to CMYK mode, save. (I assume this works in the windows version)
Command line ImageMagick will convert colour spaces and set a colour profile.
Not too sure of this one, but I think Scribus can export as CMYK. Not an application I use.

edit: a re-read of the OP
vinyl banners = big? probably the dpi will be 72 or maybe smaller if the banners are huge. 5' x 2' not huge so 72 dpi = 4320 pix x 1728 pix If the banner was to viewed at a distance of say 6' then 'rule-of-thumb' gives 95 dpi.

And another thought on 772 dpi, if not a typo then maybe it is the printing dpi which is not the same as the image dpi, example, for a photograph usually you use 300 ppi (pixels per inch) for the image but your inkjet printer will print at 600 or 1200 dpi

Which CMYK profile to use. Really, that is for the printing company to specify and sometimes to provide.

Now this is the kind of detail I like


I would agree that 772dpi seems like overkill. I will stick to 300dpi at the most. They are photo quality banners and the samples sent look flawless, but what I am printing is not really that HQ, and doesn't really need to be.


So...

It would be clever to upgrade to Gimp 2.8 Partha version which comes with the separate+

OR


Install Krita for windows, open a RGB image, change to CMYK mode, save. <<< Sounds too simple! Hahaha

Where can i get the latest windows copy of Krita?


One MASSIVE problem I am wary of is the image contains a photo of a face! I know RGB to CMYK can mess up colours, any advice???

The best thing to do is prepare your color space with ICC profiles before you begin, the conversion from RGB to CMYK will be less painful, along with the other info here, GIMP - Technical Graphical questions
Color Management with GIMP
Install Adobe ICC Profiles, in Gimp | Preferences | Color Management (You probably already have .icc profiles on your computer).

CMYK icc profiles, lots and lots of them.

Your 'AGFA : Swop Standard' (from PS I think) might well be enough, otherwise try
http://www.eci.org/en/downloads
about a third of the way down look for ISO Coated v2 300% ECI and eci_offset_2009.zip.
As good a general cmyk profile as any.

Never done any vinyl printing so I had a look around.
I think this one will be typical ..bannerofchina dot com..

This is what it says about format.
Set up image in CMYK format. Setup files at 300 dpi @ 1/3 scale, 100-150 dpi at full scale. Minimum acceptable level is 72 DPI at full size.

There is mention of colour matching (colors might be different), no reference to a specific color profile.

Gimp or Krita - why not both?
This is a screen shot of separate+ verus krita (with inset RGB) http://i.imgur.com/yjdRNZD.jpg not much difference in CMYK. This has colour management in force. I do use a monitor .icm profile and I do have the monitor brightness turned down to give a more accurate representation of printing.

If you already have a proof, great. If not, get one before ordering $$$$ of them.

Change in colours? see http://www.rgb2cmyk.org/about.html